This invention relates to methods for eliminating or controlling pest populations, and more particularly to such a method which utilizes a vitamin D compound in a high calcium bait diet.
It is well known that annually rodents are responsible for the loss of as much as 10% of the grain crop in the United States and as much as 30% of the grain crop in underdeveloped countries. Rodents are also known to transfer disease, are destructive and contaminate the food supply. Many methods have been devised for eliminating and/or controlling rodents and other vertebrate pests such as starlings and blackbirds.
The most important rodenticide in recent years has been the anticoagulant series especially warfarin, sodium warfarin, and crystalline sodium warfarin. Warfarin has had the advantage of being difficult to detect in the bait, is not immediately lethal, and thus allows the animal to consume warfarin-containing bait successively and not associate the consumption of that bait with death. It has, however, significant secondary toxicity, i.e. animals poisoned with warfarin can transmit that poison upon consumption by larger animals, as for example a cat consuming rodents poisoned with warfarin. In addition, strains of rats have developed warfarin resistance.
A recent rodenticide has been the use of vitamin D which at high doses is toxic to vertebrate animals. Doses of 750 parts/million or higher are required before vitamin D.sub.2 or vitamin D.sub.3 will cause intoxication. Although this concentration may lead to some detection, it is low enough to be effective. The vitamin D compounds are also of considerable interest in this respect, in that they do not survive for long periods of time in the environment and hence do not present an environmental problem.
A recent important advance has been the development of 1-hydroxylated vitamins since they have much higher toxicity than ordinary vitamin D. Doses of about 15 parts/million is effective against mice, rats, and other rodents, thus eliminating possible detection since it is a tasteless compound and active in small amounts. It has the advantage of being rapidly metabolized and thus provides no secondary toxicity. Furthermore because it is present in small amounts, it is even less of an environmental problem than vitamin D itself. The most important consideration is the higher potency may well reduce the cost of the vitamin D rodenticide. A method of activating vitamin D by 1-hydroxylation has also been introduced, primarily to reduce the cost of manufacturing of 1-hydroxyvitamin D.sub.3.
Rats often consume high calcium diets quite intensely. In fact, cheese must be regarded as one of the favored foods available to rats and mice. We have learned that the toxicity of vitamin D compounds is greatly increased when calcium intakes are elevated. Vitamin D compounds can therefore be made into superior rodenticides by merely providing them in a high calcium matrix or a high calcium bait diet. This invention, therefore, teaches that a superior method of eliminating pests is to provide a vitamin D compound in a high calcium bait diet. The vitamin D compound can be vitamin D.sub.3, vitamin D.sub.2, 1 alpha-hydroxyvitamin D.sub.3, 1 alpha-hydroxyvitamin D.sub.2, 25-hydroxyvitamin D.sub.3, 1 alpha, 25-dihydroxyvitamin D.sub.3, 1 alpha, 25-dihydroxyvitamin D.sub.2, and others as well as the many new analogs which are 1 alpha-hydroxylated, as defined further herein.